Diverse diets and low‐fiber, low‐tannin foraging preferences: Foraging criteria of Tibetan macaques (Macaca thibetana) at low altitude in Huangshan

Abstract Nutrient composition and food availability determine food choices and foraging strategies of animals, while altitude and geographical location affect species distribution and food availability. Tibetan macaques (Macaca thibetana) have sophisticated foraging strategies as the largest species in Macaca. They are important in understanding the ecological evolution of the entire genus. However, the mechanism of food selection in Tibetan macaques at low altitudes remains unclear. In this study, we researched a wild Tibetan macaques group (Tianhu Mountain Group, 29 individuals) living in a low‐altitude area around Mt. Huangshan, Anhui Province, China. We used instantaneous scan sampling to observe these macaques' foraging behavior from September 2020 to August 2021. We recorded the dietary composition and food availability, compared the nutrient content of staple food and non‐food items, and analyzed the role of key nutrients in food selection. We found that Tibetan macaques forage on 111 plants belonging to 93 genera and 55 families. The food types included fruits (52.5%), mature leaves (17.0%), bamboo shoots (14.4%), young leaves (6.3%), flowers (4.5%), others (2.1%), stems (1.9%), and tender shoots (1.3%). Tibetan macaques forage for a maximum of 76 plant species during spring. However, dietary diversity was highest during summer (H′ = 3.052). Monthly fruit consumption was positively correlated with food availability. Staple foods are lower in fiber, tannin, and water than non‐foods. In addition, the time spent foraging for specific foods was negatively correlated with the fiber and tannin content of the food. The results showed that Tibetan macaques' foraging plant species and food types were diverse, and their foraging strategies varied seasonally. Our findings confirmed the effect of nutrients on food choice in Tibetan macaques. We highlighted the important role of fiber and tannin in their food choices and suggested that the foraging behavior of Tibetan macaques is highly flexible and adaptive.


| INTRODUC TI ON
Nutrient composition and food availability determine food choices and foraging strategies (Lambert & Rothman, 2015). Therefore, an appropriate diet is essential for animals. The dietary structure is a complex and variable combination of nutrients that has diverse functional implications for the consumer (DeCasien et al., 2017;Vincze et al., 2022). Most natural foods do not provide a balanced diet; some have a surfeit of nutrients and a dearth of others . Therefore, animals must optimize their foraging strategies to adapt to temporal and spatial changes in the environment to improve their ecological adaptability.
Animal foraging strategies are based on finding and consuming essential nutrients while avoiding the adverse effects of plant secondary metabolites (Lambert, 2007;Simpson et al., 2004). Nutrition plays a critical regulatory role in species-environment interactions (Grainger et al., 2020). Currently, the following five theoretical hypotheses in nutritional ecology exist for explaining nutrient foraging strategies. (1) The energy maximization hypothesis holds that animals seek to maximize their energy intake. In other words, total energy is the most important nutritional variable in animal foraging (Schoener, 1971); (2) The nitrogen (protein) maximization hypothesis states that animals choose food in the mode of nitrogen (protein) maximization (Mattson, 1980); (3) According to the regulation and avoidance hypothesis of plant secondary metabolites, animals generally avoid the intake of toxic secondary metabolites (Freeland & Janzen, 1974); while (4) according to the limitations on the intake of dietary fiber hypothesis, animal feeding is affected by the fiber content of plants (Milton, 1979); (5) Finally, the nutrient balance hypothesis holds that animals balance their nutrition by mixing different foods with different nutrients, rather than maximizing the availability of one nutrient . However, these hypotheses do not apply to all primates. Foraging behavior in different primate species is specific and complex, and requires detailed analysis for different situations.
Plant productivity is lower at temperate latitudes than at tropical latitudes (Cramer et al., 1999). The temperate areas are dominated by evergreen forests and fruit availability is relatively low (Hanya & Chapman, 2013). Therefore, the same species may show different foraging preferences in different climate zones. For example, the Assamese macaque (M. assamensis) in tropical forests forages more fruits, whereas those in temperate forests forage more leaves (Ahsan, 1994;Heesen et al., 2013).
Altitude also affects food resource distribution. Previous studies have shown that temperature and biodiversity change with altitude.
Primates adapt to these changes by altering their foraging strategies.
For example, in Rhesus macaque (M. mulatta), the number of plant species consumed ranges from 102 species at 225 m, to 35 species at 2360 m (Feeroz, 2012;Goldstein & Richard, 1989;Peng et al., 2008;Tang et al., 2016;Tomar & Sikarwar, 2014). Macaques in lowland forests feed mainly on fruit and animal matter, whereas populations in alpine forests feed more on foliage and items such as bark and fungi (Tsuji et al., 2013).
Proteins are crucial functional substances in living organisms and are the only source of dietary nitrogen. Many primates tend to forage for foods high in protein and low in fiber (Ganzhorn et al., 2017), as evidenced by M. assamensis , White-footed sportive lemur (Lepilemur leucopus) (Dröscher et al., 2016), C. guereza (Fashing et al., 2007) and N. nasutus (Ma et al., 2017). This is because the fiber content can affect food palatability and reduce digestion efficiency (Barboza et al., 2010). Carbohydrates are a primary source of energy in animals. Many primates enjoy fruit because of their high sugar content. Studies of captive Western lowland gorillas (Gorilla gorilla gorilla) and Chimpanzees (Pan troglodytes) show a preference for foods with high sugar content, despite their different body sizes (Remis, 2002). Mountain gorillas (G. beringei) in Uganda also show a foraging preference for high-carbohydrate fruits (Rothman et al., 2006). Lipids are also an important source of energy for the organism, which can provide twice the energy of sugar and protein per gram (Righini et al., 2015). Lipids also provide essential fatty acids and are involved in the synthesis of other substances . Therefore, fat has an important effect on the food choices of animals. For example, in the study of black howler monkeys, there was a significant positive correlation between food choices and lipids during cold and dry seasons (Righini et al., 2015).  (Li & Kappeler, 2020;Wada et al., 1987). Body size constrains primate food selection (Ford & Davis, 1992). Tibetan macaques must have sophisticated foraging strategies to ensure sufficient energy for maintaining their large body size and adapting to cold environments. In previous studies, the Tibetan macaque was found to be a folivore primate (Thierry, 2007;Zhao, 1996). Studies have found that Tibetan macaques feed on 50 plant species at Mt. Huangshan and 196 at Mt. Emei, with significant seasonal differences (You et al., 2013;Zhao et al., 1991). However, these studies did not delve into the role of nutrient composition in foraging selection. They did not analyze the foraging and nutritional strategy of macaques. Detailed data on the nutritional strategy of Tibetan macaques are not yet available. Further study of the foraging choice of macaques under natural conditions is necessary to reflect the foraging strategy more truly and reveal their adaptability to different habitats. This study will fill the gaps in foraging nutrition strategies in Tibetan macaques. It is beneficial for proposing more effective measures for protecting Tibetan macaques and has some significance for revealing the foraging strategy of the whole Macaca genus.
In 2018, we discovered a group of wild Tibetan macaques in a low-altitude area (200-600 m) near the east gate of Mt. Huangshan and started tracking them in 2019. As a typically high-altitude dwelling species, we expect low-altitude Tibetan macaques to forage differently than those at higher altitudes, yet we lack data for lowaltitude Tibetan macaques. In this study, we aim to (1) identify the dietary composition and seasonal changes in Tibetan macaques and analyze the relationship between foraging choice and food availability, (2) measure and compare the nutrient content of food and non-food, and (3) analyze the effects of different nutrients on the feeding time of Tibetan macaques. We expected to determine the Tibetan macaques' diet and the nutritional factors that influence their foraging choices by testing the following predictions: (i) Significant differences exist in the number of plant species foraged by the same primate species living in different spatial and temporal environments. Areas at lower elevations have higher biodiversity and resource availability. Therefore, we predict that Tibetan macaques at lower altitudes will forage for as many different plant species as possible and that there will be seasonal differences in foraging plants.
(ii) Due to the higher productivity of ecosystems at lower elevations, we predict that Tibetan macaques tend to prefer highquality foods and will forage more for fruit when fruit abundance is higher.
(iii) Based on the nitrogen (protein) maximization model, plant secondary metabolites avoidance model, and the limitation of the dietary fiber model, we predicted that Tibetan macaques in lowaltitude habitats would forage for more high-protein, low-fiber, and low-tannin foods when faced with relatively abundant food resources.
(iv) Tibetan macaques require more energy to meet their physical needs as the largest primate of the genus Macaca. We predict that Tibetan macaques will select foods high in sugar and fat.

| Study site and animals
This study was conducted in the Niejiashan area (30°12′N, 118°27′ E,  Center. This area has a subtropical monsoon climate zone and four distinct seasons. The total annual rainfall is 2639.4 mm, and the average annual temperature is 15.5°C, with a maximum of 38.1°C and a minimum of −13.1°C. Following Li et al. (2021), the four seasons were defined according to the monthly average temperature. An average temperature greater than 22°C is classified as summer (June-September), <10°C as winter (December-February), and 10-22°C as spring (March-May) and autumn (October-November) (Li et al., 2021).
We studied a group of 29 wild Tibetan macaques (Figure 1), including 5 adult males, 8 adult females, 10 juveniles, and 6 infants. We can distinguish age according to body size and the shade of hair color.
These macaques spent extensive time at altitudes below 600 m.

| Behavioral data collection
The fieldwork began in August 2019 and ended in August 2021. We set up 30 automatic return infrared cameras (UML4, UOVISION) in the Tibetan macaques' habitat to identify the movement of the monkeys and to search for and track the monkeys based on those positions. Owing to the impact of COVID-19, the data we collected were discontinuous during the first year. After a year of tracking and habituation, we had a home range for the group and were able to keep the data continuous.
We arrived at the Tibetan macaque's sleep site every morning before 6 o'clock. After locating the macaques, we used our phones' Liangbulu (Shenzhen Liangbulu Information Technology Co., Ltd.) GPS software to collect the group's geographical location. We then observed their behavior until they disappeared for 30 min or entered the sleeping place in the evening. We obtained continuous data from September 2020 to August 2021 and analyzed these data.
We used the instantaneous scanning sampling method to collect data (Altmann, 1974), with each scan lasting 5 min and a 5-min interval between scams. We observed Tibetan macaques using binoculars (PROSTAFF7, Nikon) at distances of 20-100 m and used a voice recorder (ICD-PX470, SONY China) to record the data. To avoid sampling bias for specific individuals, as many individuals as possible were scanned from left to right at each sampling time. We observed each individual for 5 s during each scan and recorded their primary behaviors (classified as resting, moving, feeding, socializing, etc.). When individuals ate, we recorded the species and parts of the plants they ate, including mature leaves, young leaves, flowers, fruits, stems, tender shoots, and others. Because the foraging frequency of bamboo shoots was relatively high, and classification is complicated, bamboo shoots were listed separately as a food type. We also used ad libitum sampling to record the F I G U R E 2 Study site (the study site was situated at the boundaries of the Huangshan Mountains and Tianhu nature reserve. The range of the black coil shown here is the home range of the Tibetan macaque). species of food plants between scans to obtain the diet composition (Altmann, 1974) but these data were not used for analysis.
During the study period (September 2020 to August 2021), we obtained 32,914 individual records from 3034 scans, with an average of 10.85 individuals per scan (Table 1).

| Samples collection
We collected 81 samples (three samples per item) from 27 items of 23 plants, including 15 main food types and 12 dominant non-food species in the environment ( Table 2). To obtain the data on dominant vegetation species in the Tibetan macaques' home range, we set 33 20 × 20 m quadrats and 64 × 100 m transect zones according to the elevation gradient in the macaque home range from September 2019 to November 2019. The trees, shrubs, herbs, and vines were counted and identified (Li et al., 2021). We calculated the proportion of each food item in all feeding records, defining foods that accounted for 1% or more as important. When we observed macaques foraging for a certain plant, we collected 500 g from the same plant after the individuals left. Due to the complexity of field sampling, we were unable to collect important food samples from dangerous terrains. Samples of dominant species were collected in the same manner. Samples were then prepared for nutritional analysis, described below.

| Food availability assessment
Based on the results of the first year (August 2019 to August 2020), 35 plants were selected for phenological monitoring. We randomly selected 10 plants of each species from the main range of Tibetan macaques and monitored them in the middle of each month. We recorded the growth of the mature leaves, young leaves, flowers, fruits, and tender shoots. Quantitative statistics were performed by estimating the proportion of individual food types to the canopy volume of the plants. To facilitate the estimation and ensure the relative accuracy of the value, we divided the sub-ratio into five levels: 0 < 1%, 1 = 1%-25%, 2 = 26%-50%, 3 = 51%-75%, and 4 > 75%. The following formula was used to calculate the availability of individual foods per month (Silver et al., 1998).
where C i is the sum of the thorax height area of the instant feeding species i and V is the mean ratio of i to the crown volume per tree in a certain month. The sum of the same food types is the availability of this food type.

| Nutritional analysis
All samples were weighed to determine the fresh weight (W t ).
The samples were then baked in a 105°C thermostatic drier box  (Bradford, 1976). Total sugar was measured using the 3,5-dinitrosalicylic acid assay (Dubois et al., 1956). Starch was measured using the enzymatic hydrolysis method (Standardization Administration of the People's Republic of China, 2016). Fiber content was measured using anthrone colorimetry (Li et al., 2018).

| Data analysis
Following Shaffer (2013) and Huang et al. (2015), we first divided the number of individuals foraging for a particular food in each scan by the number of individuals recorded in that scan and then divided this value by the proportion of individuals engaged in feeding activity in the scan to indicate the percentage of foraging time for a particular food. The average of all scans over an hour represents the time spent foraging for a specific food per hour. To correct deviations that may result from uneven scanning records throughout the day, we averaged the hourly data to represent the daily feeding time of certain foods. The average daily data were used to indicate the monthly feeding time on specific food items. The average monthly data were then used to determine the time of the year when certain foods were consumed.
We used the Shannon-Wiener diversity index to express the dietary breadth of Tibetan macaques, H � = − ∑ n i=1 PilnPi (Pi is the percentage of feeding records of plant species i) (Huang et al., 2015).
We tested all variables using a one-sample Kolmogorov-Smirnov test to examine normality. We used Pearson's and Spearman's correlations to examine the relationship between consumption of different food types and the relationship between food type consumption and food availability. All tests were two-tailed, with a significance of .05.
To improve linearity, logit (X) transformation was applied to variables expressed as percentages, such as water, protein, fiber, total sugar, starch, crude fat, and tannin. Logit (X + 0.00001) transformation was applied to feeding time because the original data of feeding time for non-food species were 0 (Warton & Hui, 2011).
We constructed a generalized linear mixed model (GLMM) to examine the differences in nutrient composition between food and non-food. In the model, the contents of water, fat, protein, fiber, sugar, starch, and tannin were set as the response variable, respectively, plant type (food or non-food) was set as a fixed factor, plant parts and plant species were set as random factors. We then compared the models with and without fixed factors using anova (analysis of variance) for determining the influence of fixed factors on the dependent variables. When p < .05, the fixed factor significantly affected the goodness of fit of the model, indicating that there were significant differences in response variables between food and no-food.
We constructed GLMMs to study the effects of different nutrients on feeding time. We set the annual feeding time of plants as the response variable, the nutrient composition as fixed factors, and the plant species and parts as random factors in the model.
We obtained 2 7 -1 = 127 models from all possible combinations of the 7 fixed factors, and multi-model reasoning and model averaging were conducted based on information theory (Akaike's information criterion corrected for small sample sizes, AICc). In the model construction process, 7 nutrients (water, fiber, fat, protein, total sugar, starch, tannin) were screened into the model and the "glmulti" function was used to screen all possible models and select the optimal model. The models were sorted according to important food sources, accounting for 80.58% of the total consumption of Tibetan macaques (Table 3).

| Seasonal variations in diet
The number of food species consumed and dietary diversity

| Effects of nutrients on feeding time
The two most supported models (ΔAICc ≤ 2) included four variables: fiber, starch, total sugar, and tannin. The Akaike weight (W i ) values of the two most supported models were 0.18 and 0.07, respectively (Table 6).
Model averaging showed that fiber (W ip = 0.74) and tannin (W ip = 0.59) were significant factors affecting feeding time in Tibetan macaques ( Table 7). The model-averaged 95% confidence intervals of these two predictors never overlapped with zero. Feeding time decreased (β < 0) with increasing fiber and tannin. Although total sugar and starch were included in the two highly supported models (ΔAICc ≤ 2;

| DISCUSS ION
Dietary composition and nutrition are essential factors for understanding foraging strategies in primates. We studied the foraging strategies of Tibetan macaques in low-altitude habitats by analyzing their diets and the effects of nutrients on their foraging choices. Our study found that Tibetan macaques at low altitudes forage for more unique plant species than Tibetan macaques at high altitudes in the same area (54 species, Wang, 2008; 50 species, You et al., 2013), and the number of food species is different in season. This is consistent with our prediction i. Altitude differences can lead to differences in species richness and food availability. Studies have shown that temperature and biodiversity change with altitude, with resources being more abundant at lower altitudes (Kӧrner, 2003). In this study, Tibetan macaques foraged heavily for foods not recorded in studies at high altitudes, such as Stauntonia brachyanthera. The number of species of food plants of macaques distributed on Mt. Emei (1260-2100 m above sea level) was higher than those in this study (196 species, Zhao et al., 1991), which may be due to the difference in geographical locations. Mt.

TA B L E 4 Number of food species and dietary diversity of Tibetan macaques in different seasons
Emei has a high species richness. The vegetation types include evergreen broad-leaved forest, evergreen deciduous broad-leaved mixed forest, and evergreen coniferous forest (Zhao et al., 1991).

F I G U R E 4
Comparison of nutritional components among food and non-food (food: N = 15; non-food: N = 12. χ 2 test: *p < .05). and Colobinae, wherein differences in geographical location and altitude led to differences in diet composition (Britt et al., 2002;Tsuji et al., 2013). Studies on Golden monkey (Cercopithecus mitis kandti) found that they also adjust their diet based on habitat and food availability (Tuyisingize et al., 2021). Previous studies have defined Tibetan macaques as folivore primates (Thierry, 2007;Wang, 2008;Zhao, 1996), but the findings of the current study provide a different perspective. We found that fruit feeding in Tibetan macaques is influenced by environmental food availability. When the fruit is plentiful, macaques reduce the consumption of other plant parts.
This is consistent with our prediction ii. Owing to the effect of cold climates, fruit richness in high-altitude areas is lower than that in low-altitude areas (Glowacka et al., 2017;Kӧrner, 2003). Studies on G. beringei beringei established that elevation can lead to dramatic changes in diet, with more fruits consumed at lower altitudes than at higher altitudes (Ganas et al., 2004). The time spent foraging for fruits in baboons also decreases with elevation (Hill & Dunbar, 2002). This suggests that a broad dietary strategy cannot accurately classify primate feeding habits. Therefore, our results suggest that food availability is a crucial factor that affects the diet of Tibetan macaques. Some primates cannot be directly classified as folivores or frugivores.
Analysis of the nutritional content of food and non-food items revealed that the contents of fiber, tannins, and water in foods were lower than those in non-food items. The foraging choice of macaques was consistent with the dietary fiber restriction hypothesis and secondary metabolite avoidance hypothesis, in line with our prediction (iii). Fibers affect digestion efficiency and reduce food palatability (Barboza et al., 2010). Therefore, many primates avoid foods that are high in fiber. For example, red colobus monkeys (Procolobus badius), C. guereza, and N. nasutus show high selectivity for foods with low fiber content (Chapman & Chapman, 2002;Fashing et al., 2007;Ma et al., 2017). Tannins can bind to proteins, thereby affecting the digestibility of food and nutrient absorption (Wink, 2003). Studies on Bornean orangutans (Pongo pygmaeus), C. guereza, and M. assamensis have found that these primates avoid tannin-rich foods (Fashing et al., 2007;Leighton, 1993;. Tibetan macaques chose plants with low fiber and tannin contents in this study. As mentioned above, Tibetan macaques foraged more fruits in this study. Fruit tends to have lower fiber and tannin content than mature leaves and other plant parts, which partly explains the low fiber and tannin content in their diet. Water is essential in the processes of thermoregulation and many primates choose juicy foods to meet their water requirement . However, the water content in Tibetan macaques' food items was lower than that in non-food items. There are abundant surface water resources in the habitat of Tibetan macaques, and small streams or reservoirs can be seen everywhere. Tibetan macaques have been observed to directly go to water sources for meeting their drinking needs; therefore, water in food is not crucial for them. Individuals of the species G. beringei are also known to drink from streams to meet their water requirements (Rothman et al., 2008). Therefore, our results suggest that Tibetan macaques may be inclined to choose foods with low fiber and tannin content and water may not be a limiting factor in their food choices.
Surprisingly, our study found that protein was excluded from all highly supported models and there was no difference between food Abbreviations: AICc, Akaike's information criterion corrected for small sample sizes; ΔAICc, the difference between a specific model and the most high-ranked one; W i (Akaike weights), the probability that a model is optimal given the particular set of models considered.

TA B L E 6
The top two linear regressions models (lm) (ΔAICc ≤ 2) investigating the effects of nutrient content on the feeding effort of Tibetan macaques. TA B L E 7 Summary of model averaging based on lm models using nutrient factors to explain the feeding time of Tibetan macaques on specific food. and non-food. This does not support our predictions (iii). This is different from other studies, for example, in which L. leucopus (Dröscher et al., 2016) and M. assamensis   Proteins are more restricted in protein-deficient environments. In other words, Tibetan macaques can easily get the protein they need from a variety of foods, without having to seek out high-protein foods.
Fat, sugar, and starch are important sources of energy (National, 2003). G. gorilla gorilla, P. troglodytes, White-bellied spider monkeys (Ateles belzebuth), and N. nasutus, all vary in size but enjoy a diet high in sugar, especially ripe fruit (Ma et al., 2017;Remis, 2002;Stevenson & Link, 2010), while A. pigra (Righini et al., 2015) opts for high-fat foods. What was different in our study was that there were no significant differences in fat, total sugar, and starch content between Tibetan macaques' staple foods and non-food. Although total sugar and starch were included in the highly supported models (ΔAICc ≤ 2; Table 6), their model-averaged 95% confidence interval of the regression coefficient (β) contained zero. This is not consistent with our prediction (iv). Species richness and resource availability are high in the low-altitude habitats of Tibetan macaques (Li et al., 2021). Abundant food resources in low-altitude habitats give Tibetan macaques great freedom in food choice. They can get enough food to satisfy their body's needs with minimal expenditure instead of seeking out foods high in fat and sugar. As a result, they can meet their needs while avoiding excessive intake of nutrients such as tannins and fiber that are bad for digestion and absorption.
The low-fiber and low-tannin foraging strategy may be an adaptation for Tibetan macaques to the abundance of resources in lowaltitude habitats.
In summary, our study found that the foraging behavior of Tibetan macaques is highly flexible and adaptable. They change their foraging strategies in response to environmental changes both spatially and temporally. Tibetan macaques living at low altitudes prefer low-fiber and low-tannin foods. This diverse dietary preference adapts to higher species richness in low-altitude habitats and may provide the energy necessary for Tibetan macaques to maintain their large body size. Our findings confirmed the effect of nutrients on food choice in Tibetan macaques. We also demonstrated the complexity of primate foraging behavior in terms of nutrition, food availability, and geographical distribution. The diet of primates should be defined comprehensively rather than simply as folivore or frugivore. There were some limitations in this study. Due to the lack of individual identification of wild Tibetan macaques, the instantaneous scanning sampling method adopted in this study could not quantify the nutritional intake of macaques and the foraging data of macaques at high altitudes in the same region were lacking. Although we uncovered some of the nutritional foraging strategies of macaques, quantitative analysis is the next step. Our next goal is to analyze nutrient intake based on individual identification and collect high-altitude foraging data. As the nutrient balance hypothesis suggests, animals balance their nutrition by mixing different foods with different nutrients, rather than maximizing the availability of one nutrient . Due to their large body size, Tibetan macaques have great nutritional and energy requirements.
They may prefer a balanced intake of nutrients rather than relying on a single nutrient. Therefore, nutritional balance strategy will also be one of our future research directions. We will further quantitatively analyze the nutritional strategies of Tibetan macaques to fully reveal the adaptive strategies of their foraging behavior.

ACK N OWLED G M ENTS
We thank the management of Huangshan National Park and all the villagers of Niejiashan for facilitating and supporting our research. We thank Zhongbao Yang's family for their help with the logistical arrangements. We also thank Qixin Zhang and Zhonghao Huang for their advice on the statistical analysis. This work was supported by the National Natural Science Foundation of China (No. 31971404) and the Central Government of Anhui Province guided the development of local science and technology (No. 2019b11030018).

CO N FLI C T O F I NTE R E S T
None declared.

DATA AVA I L A B I L I T Y S TAT E M E N T
The dataset generated and analyzed during the current study is